Use of silicon compounds to dye human keratin fibres; novel compounds and compositions containing them

ABSTRACT

The use of linear or cyclic silicon compounds containing at least one chromophoric group of quinone or azo type as direct dyes in dye compositions intended for dyeing human keratin fibers and in particular the hair. The invention also relates to novel silicon compounds and dye compositions containing them, as well as to the corresponding direct dyeing process.

This is a division of application Ser. No. 08/961,261, filed Oct. 30,1997 now U.S. Pat. No. 6,007,537 which is incorporated herein byreference.

The invention relates to the use of linear or cyclic silicon compoundscontaining at least one chromophoric group of quinone or azo type asdirect dyes in a dye composition intended for dyeing human keratinfibres and in particular the hair; the invention also relates to some ofthese silicon compounds as novel compounds.

Silicon dyes have already been described and proposed for dyeingsynthetic fibres; such dyes are described in Belgian patent Nos.875,160, 875,182 and 875,230, U.S. Pat. No. 2,925,313, German patent No.2,918,685 and in European patent application No.455,595, the disclosuresof which are specifically incorporated by reference herein.

Silicon dyes have also been described and proposed for dyeing siliconeresins: see in this respect U.S. Pat. Nos. 3,838,891, 3,981,859 and4,038,293, the disclosures of which are specifically incorporated byreference herein. Silicon dyes which can be used in the manufacture ofphotosensitive polymers are also known in the prior art: see Germanpatent application No. 2,040,831, the disclosure of which isspecifically incorporated by reference herein.

For most of them, these silicon dyes are reactive on account ofhydrolysable groups carried in their structure, and they have never beenproposed for use in cosmetics.

Moreover, certain unreactive but physically and chemically inertpolysiloxane dyes of high molecular weight have been prepared, in theU.S. Pat. No. 4,381,260, the disclosure of which is specificallyincorporated by reference herein, and proposed, on account of theirstability, for uses such as the dyeing of natural textiles, of plastics,or for dyeing foodstuffs and pharmaceutical and cosmetic preparations.

However, in the field of hair dyeing, direct dyes are sought, that is tosay dyes which, without supplying an oxidizing agent, are capable bythemselves of temporarily modifying the natural shade of the hair. Inthis application, it is desired that the dyes satisfy a certain numberof criteria; they will preferably be as inoffensive as possible, that isto say that they have an acceptable level of harmlessness, and they willpreferably give rise to colorations that are sufficiently fast, inparticular with respect to light, washing, perspiration and bad weather.

Among the direct dyes conventionally used in hair dyeing, quinone dyessuch as those of anthraquinone, benzoquinone and naphthoquinone type andazo dyes are known. Not all of these dyes are entirely inoffensive,which is why, in hair cosmetics, dye molecules of this type withincreasingly higher levels of performance in terms of harmlessness aresought.

Now, after considerable research conducted in this matter, the inventorshave discovered that silicon compounds which contain at least onechromophoric group of quinone or azo type, and some of which are novel,make it possible to dye human keratin fibres such as the hair without anoxidizing agent, with the advantageous property of having an excellentlevel of harmlessness.

In addition, the hair colorations obtained using these compounds arefaster than those produced with non-silicon compounds of quinone or azotype of the prior art.

This discovery forms the basis of the present invention.

The subject of the present invention is thus the use, as direct dyes ina dye composition intended for dyeing human keratin fibres and inparticular the hair, of linear or cyclic silicon compounds containing atleast one chromophoric group of quinone or azo type, characterized inthat they correspond to one of the formulae (1), (2) or (3) below:

in which formulae (1) and (2):

R, which may be identical or different, are chosen from C₁-C₁₀ alkyl,phenyl and 3,3,3-trifluoropropyl radicals, at least 80%, in numericalterms, of the radicals R being methyl,

B, which may be identical or different, are chosen from the aboveradicals R and the radical A defined below,

r is an integer ranging from 0 to 50, and s is an integer ranging from 0to 20, with the condition that if s is zero then at least one of the twosymbols B denotes A,

u is an integer ranging from 1 to 6, and

t is an integer ranging from 0 to 10, it being understood that t+u isequal to or greater than 3,

in which formula (3):

R₁, R₂ and R₃, which may be identical or different, are chosen fromlinear or branched, saturated or unsaturated C₁-C₈ alkyl and alkenylradicals, and in which formulae (1), (2) and (3) the symbol A denotes aradical, which may be identical or different, of formula (4a), (4b),(4c) or (4d) below:

in which formulae (4a), (4b), (4c) and (4d):

R₄, which may be identical or different, represent a linear or branchedC₁-C₆ alkyl radical, OH, C₁-C₄ alkoxy, hydroxy(C₁-C₄)alkyl, COOH, CONH₂,CN, SO₃H, a halogen, an NO₂ radical, or a radical NR₅R₆ in which R₅ andR₆, which may be identical or different, denote a hydrogen atom, a C₁-C₈alkyl or hydroxy(C₁-C₄)alkyl or amino(C₁-C₄)alkyl radical, or form,together with the nitrogen atom to which they are attached, a 5- or6-membered heterocycle which may be interrupted by an oxygen or sulphuratom,

m is an integer ranging from 0 to 2,

n is an integer equal to 1 or 2,

D is an —SO₂NH—, —CONH— or —O— radical or a radical —NR₇— in which R₇ isH or CH₃,

W is a divalent radical of formula (5):

or of formula (6):

—HC═CH—(Z)_(p)—  (6)

in which formulae (5) and (6):

R₈ denotes a hydrogen atom, a hydroxyl radical or a linear or branched,saturated or unsaturated C₁-C₈ alkyl radical,

Z is a linear or branched C₁-C₆ alkylene radical optionally substitutedwith an OH radical or a linear or branched, saturated or unsaturatedC₂-C₈ alkoxy radical, and

p is an integer equal to 0 or 1.

In formulae (1), (2) and (3) above, A thus represents a quinone(anthraquinone, naphthoquinone or benzoquinone) or azo group which,after attaching to the starting silicon chains, gives the compounds offormulae (1), (2) and (3) dyeing properties.

The alkyl radicals may be chosen in particular from methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-amyl, isoamyl,neopentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl and tert-octylradicals. The alkyl radicals R and B which are preferred according tothe invention are the methyl, ethyl, propyl, n-butyl, n-octyl and2-ethylhexyl radicals. Even more preferably, the radicals R and B areall methyl radicals.

Among the linear or cyclic silicon compounds which may be used accordingto the present invention, random derivatives or derivatives withwell-defined blocks having at least one, and even more preferably all,of the following characteristics:

R is alkyl and even more preferably methyl,

B is alkyl and even more preferably methyl,

r ranges from 0 to 3 and is more preferably zero,

s ranges from 1 to 3, more preferably equal to 1,

t+u ranges from 3 to 5,

R₁, R₂ and R₃ are alkyl and even more preferably methyl,

R₈ is hydrogen, Z is methylene and p is equal to 1, are moreparticularly preferred.

According to the invention, the compounds more particularly preferredare the following:

4-(4-dimethylaminophenylazo)-N-[3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl]-propyl]benzenesulphonamide[compound (7)]:

4-(4-dimethylaminophenylazo)-N-[3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl]-propyl]benzamide[compound (8)]:

2-(4-methoxy-2-nitrophenylazo)-5-(3-trimethylsilanylpropoxy)phenol[compound (9)]:

2,5-bis[3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl]propylamino]benzoquinone[compound (10)]:

2-chloro-3-[3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl]propylamino]-[1,4]-naphthoquinone[compound (11)]:

2-[3-[(1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl]propylamino]-[1,4]-naphthoquinone[compound (12)]:

1-hydroxy-4-[3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl]propylamino]-anthraquinone[compound (13)]:

1,4-di-[3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl]propylamino]-anthraquinone[compound (14)]:

To prepare the silicon dyes of formulae (1), (2) and (3), it is possibleto work conventionally (route 1), by carrying out a hydrosilylationreaction, namely:

starting with the corresponding silicon compound, in which, for example,all the radicals A are hydrogen atoms. This starting silicon compound isreferred to hereinbelow as the SiH derivative; the SiH groups may bepresent in the chain and/or at the ends of the silicon chain. These SiHderivatives are products that are well known in the silicone industryand are widely commercially available. They are described, for example,in U.S. Pat. Nos. 3,220,972, 3,697,473 and 4,340,709, the disclosures ofwhich are specifically incorporated by reference herein.

This SiH derivative may thus be represented

either by formula (15) below:

in which R, r and s have the meanings given above for formula (1) andthe radicals B′, which may be identical or different, are chosen fromthe radicals R and a hydrogen atom,

or by formula (16) below:

in which R, t and u have the meaning given above for formula (2),

or by formula (17) below:

in which R₁, R₂ and R₃ have the meanings given above for formula (3).

A standard hydrosilylation reaction is thus carried out on this SiHderivative of formula (15), (16) or (17), in the presence of acatalytically effective amount of a platinum catalyst, on an organiccompound of formula (4a), (4b), (4c) or (4d), in which the symbol W isreplaced by the symbol (W′) which denotes a monovalent radical offormula (18) or (19) below:

in which formulae (18) and (19), Z, R₈ and p have the same meanings asin formulae (5) and (6) defined above.

Another possible synthetic route (route 2) which is suitable forpreparing silicon dyes of formulae (1), (2) and (3) comprises the stepof reacting an aminosilicon compound corresponding to formula (15), (16)or (17) defined above, but in which the hydrogen atom has been replacedby a monovalent radical of formula: —D—CH₂—CHR₈—(Z)_(p)—NH₂, in which Dhas same meanings as in formulae (4a), (4b), (4c) and (4d) defined aboveand R₈ and p have the same meanings as in formulae (5), (6), (18) and(19) defined above, on a compound of formula (20a), (20b), (20c) or(20d) below:

in which formula (20a), (20b), (20c) or (20d):

R₄, m and n have the same meanings as in formulae (4a), (4b), (4c) and(4d) defined above, and

R₉ denotes a hydrogen atom, a halogen atom or a hydroxyl radical.

Among the compounds of formula (1) of the invention, some are known perse, in particular those described in U.S. Pat. No. 4,381,260 and patentSU 1,712,374, the disclosures of which are specifically incorporated byreference herein.

Others are novel and constitute another subject of the presentinvention.

Another subject of the present invention is thus novel compounds offormula (1) defined below, and of formula (2) defined above.

The said novel compounds of formula (1) are those for which:

(i) the radicals B denote a CH₃ radical, s is equal to 1 and r denotesan integer ranging from 0 to 10, and

(ii) s denotes zero, the radicals B simultaneously denote a radical A offormula (4a), and D is other than NH.

The said compounds of formula (3) are novel except for those for which Ais a group of formula (4d), R₈ denotes hydrogen, R₁, R₂ and R₃ denotealkyl groups and D denotes a group NR₇, which are described in GB patent882,063 and U.S. Pat. No. 2,931,693, the disclosures of which arespecifically incorporated by reference herein.

The subject of the invention is also a dye composition for human keratinfibres and in particular the hair, and more particularly a direct dyecomposition for hair, comprising, in a medium which is suitable fordyeing, an effective amount of at least one compound of formula (1), (2)or (3) defined above.

However, other characteristics, aspects and advantages of the inventionwill emerge even more clearly on reading the description which follows,as well as the various concrete, but in no way limiting, examplesintended to illustrate it.

The compounds of formula (1), (2) or (3) are generally present inproportions ranging approximately from 0.01 to 10%, preferablyapproximately from 0.1 to 5%, by weight relative to the total weight ofthe dye composition.

The compounds of formula (1), (2) or (3) may also be incorporated intodye compositions for oxidation dyeing which contain oxidation bases andoptionally couplers, in order to enrich with glints the shades obtainedwith the oxidation dyes.

The medium which is suitable for dyeing is, in this case, preferably amedium comprising water and/or cosmetically acceptable organic solvents,and more particularly alcohols (ethyl alcohol, isopropyl alcohol, benzylalcohol and phenylethyl alcohol), glycols or glycol ethers (propyleneglycol or ethers thereof such as, for example, propylene glycolmonomethyl ether, butylene glycol and dipropylene glycol, as well asdiethylene glycol alkyl ethers such as, for example, diethylene glycolmonoethyl ether or monobutyl ether, and ethylene glycol monomethyl,monoethyl and monobutyl ethers), in concentrations ranging approximatelyfrom 0.5 to 20%, and preferably approximately from 2 to 10%, by weightrelative to the total weight of the composition.

The said dye composition may also contain any other adjuvant commonlyused in dyeing human keratin fibres and, for example, surfactants thatare well known in the state of the art and of anionic, cationic,nonionic, amphoteric or zwitterionic type or mixtures thereof,thickeners, antioxidizing agents, fragrances, sequestering agents,dispersing agents, conditioners, preserving agents, opacifiers, etc.

Obviously, a person skilled in the art will take care to select theoptionally additional compound(s) mentioned above such that theadvantageous properties intrinsically associated with the dyecomposition according to the invention are not, or not substantially,adversely affected by the addition(s) envisaged.

The dye composition according to the invention may be formulated atacidic, neutral or alkaline pH, it being possible for the pH to range,for example, from 4 to 11 and preferably from 5 to 10, and it beingpossible for this pH to be adjusted using basifying or acidifying agentsthat were well known previously.

Among the basifying agents which may be mentioned, by way of example,are aqueous ammonia, alkaline carbonates, alkanolamines such as mono-,di- and triethanolamine as well as derivatives thereof, sodiumhydroxide, potassium hydroxide and compounds of the following formula:

in which R is a propylene residue optionally substituted with a hydroxylgroup or a C₁-C₄ alkyl radical, and R₁₀, R₁₁, R₁₂ and R₁₃, which may beidentical or different, represent a hydrogen atom, a C₁-C₄ alkyl radicalor a C₁-C₄ hydroxyalkyl radical.

The acidifying agents are conventionally, by way of example, inorganicor organic acids such as hydrochloric acid, orthophosphoric acid,carboxylic acids such as tartaric acid, citric acid or lactic acid, orsulphonic acids.

The composition applied to the fibres may be in various forms, such asin the form of a liquid, a cream, a gel or any other form which issuitable for preparing a dye for keratin fibres. In particular, it maybe packaged under pressure in an aerosol can in the presence of apropellant and may form a foam.

Another subject of the invention relates to a process for dyeing humankeratin fibres, and in particular the hair, by direct dyeing, thisprocess comprising the step of leaving a dye composition containing atleast one compound of formula (1), (2) or (3) on the wet or dry keratinfibres. The composition according to the invention may be used as aleave-in composition, that is to say that after the composition has beenapplied to the fibres, they are dried without intermediate rinsing. Inthe other modes of application, the composition is left to act on thefibres for an exposure time ranging approximately from 3 to 60 minutes,preferably approximately from 5 to 45 minutes, after which the fibresare rinsed, optionally washed and rinsed again, and then dried.

Concrete examples illustrating the invention will now be given.

PREPARATION EXAMPLES Example 1

Preparation of4-(4-dimethylaminophenylazo)-N-[3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]-disiloxanyl]propyl]benzenesulphonamide:

4-Dimethylamino4′-azobenzenesulphnyl chloride (3.23 g, i.e. 0.01 mol)was added portionwise to a refluxing (40° C.) mixture ofheptamethylamino-propyltrisiloxane (3.07 g, i.e. 0.011 mol),triethylamine (1.11 g, i.e. 0.011 mol) and dichloromethane (10 ml); themixture was refluxed for 3 hours and then cooled. The reaction mixturewas poured into 30 ml of water. The organic phase was washed with waterand then dried over sodium sulphate. After recrystallization frommethanol, compound (7) was obtained in the form of an orange-colouredpowder.

m.p.: 82° C.

UV (ethanol) λ_(max=)432 nm, ε_(max)=37 350.

Elemental analysis for C₂₄ H₄₂ N₄ O₄ S Si₃

theory: C50.85 H7.47 N9.88 S5.66 Si14.86 found: C50.53 H7.54 N9.85 S5.51Si14.90

Example 2

Preparation of4-(4-dimethylaminophenylazo)-N-[3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]-disiloxanyl]propyl]benzamide:

4-Dimethylaminoazobenzene-4′-carboxylic acid chloride (3.24 g, i.e. 0.01mol) was added portionwise to a refluxing (40° C.) mixture ofheptamethylamino-propyltrisiloxane (6.15 g, i.e. 0.022 mol),triethylamine (2.2 g, i.e. 0.022 mol) and dichloromethane (20 ml); themixture was refluxed for 2 hours and then cooled. The reaction mixturewas poured into 50 ml of water. The organic phase was washed with waterand then dried over sodium sulphate. The crude product was purified bycolumn chromatography (eluent: CH₂Cl₂). Compound (8) was thus obtainedin the form of an orange-coloured powder.

m.p.: 187° C.

UV (ethanol) λ_(max)=428 nm, ε_(max)=33 500.

Elemental analysis for C₂₅ H₄₂ N₄ O₃ Si₃

theory: C56.56 H7.97 N10.55 Si15.87 found: C56.32 H7.97 N10.47 Si16.10

Example 3

Preparation of2-(4-methoxy-2-nitrophenylazo)-5-(3-trimethylsilanylpropoxy)phenol:

A mixture of 4-(4-methoxy-2-nitrophenylazo)benzene-1,3-diol (2.5 g, i.e.0.0086 mol) and potassium carbonate (1.24 g) in 30 ml ofdimethylformamide was brought to 70-75° C. 3-Chloropropyltrimethylsilane(1.24 g, i.e. 0.0086 mol) was added thereto over 20 minutes. The mixturewas stirred at 75° C. for 6 hours. The reaction mixture was then pouredinto 50 ml of water and extracted with diisopropyl ether. The organicphase was dried, concentrated and purified by column chromatography(eluent: 50/50 heptane/CH₂Cl₂) to give compound (9) in the form of a redpowder.

m.p.: 128-129° C.

UV (ethanol) λ_(max)=409 nm, ε_(max)=21 950.

Elemental analysis for C₁₉ H₂₅ N₃ O₅ Si

theory: C56.56 H6.24 N10.41 Si6.96 found: C56.18 H6.12 N10.46 Si6.69

Example 4

Preparation of2,5-bis[3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl]propylamino]-benzoquinone:

A mixture of benzoquinone (3.24 g, i.e. 0.03 mol),heptamethylaminopropyltrisiloxane (5.6 g, i.e. 0.02 mol) and ethanol (40ml) was refluxed for 1 hour. The solvent was removed under vacuum andthe residue was then taken up in 50 ml of heptane. The mixture wasfiltered to remove the hydroquinone formed and was purified by columnchromatography (eluent: 50/50 heptane/CH₂Cl₂). Compound (10) was thusobtained in the form of a red powder.

m.p.: 124° C.

UV (ethanol) λ_(max)=341 nm, ε_(max)=30 095. λ_(max)=494 nm,ε_(max)=400.

Elemental analysis for C₂₆ H₅₈ N₂ O₆ Si₆

theory: C47.08 H8.81 N4.22 Si25.41 found: C46.86 H8.76 N4.23 Si25.80

Example 5

Preparation of2-chloro-3-[3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl]propylamino]-[1,4]-naphthoquinone:

2.27 g, i.e. 0.01 mol, of 2,3-dichloronaphthoquinone in 30 ml ofdichloromethane were brought to reflux.Heptamethylaminopropyltrisiloxane (11.2 g, 0.04 mol) was added theretoover 20 minutes and the mixture was refluxed for 1 hour. Afterconcentration of the reaction medium, the solid formed wasrecrystallized from methanol. Compound (11) was obtained in the form ofa red powder.

m.p.: 80-81° C.

UV (ethanol) λ_(max)=475 nm, ε_(max)=3 850.

Elemental analysis for C₂₀ H₃₂ Cl N O₄ Si₃

theory: C51.09 H6.86 C17.54 N2.98 Si17.92 found: C50.72 H6.89 C17.43N3.12 Si18.28

Example 6

Preparation of2-[3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl]propylamino]-[1,4]-naphthoquinone:

Naphthoquinone (4.74 g, i.e. 0.03 mol) andheptamethylaminopropyltrisiloxane (5.58 g, i.e. 0.02 mol) in ethanol (40ml) were refluxed for 4 hours. After concentrating the reaction mixtureto half its volume, the solid formed was isolated. Compound (13) wasobtained in the form of an orange-coloured powder.

m.p.: 95-96° C.

UV (ethanol) λ_(max)=452 nm, ε_(max)=3 850.

Example 7

Preparation of1-hydroxy-4-[3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl]propylamino]-anthraquinone:

Leucoquinizarine (4.12 g, i.e. 0.017 mol) andheptamethylaminopropyltrisiloxane (11.88 g, i.e. 0.0425 mol) intetrahydrofuran (40 ml) were refluxed for 3 hours. After cooling, astream of air was bubbled through the reaction mixture for 2 hours.After column chromatography (eluent: 50/50 heptane/CH₂Cl₂), a mixture ofcompounds (13) and (14) was obtained. By crystallization of this mixturefrom 60 ml of methanol, compound (13) was recovered in the form of aviolet powder.

m.p.: 71-72° C.

UV (ethanol) λ_(max)=557 nm, ε_(max)=13 100. λ_(max)=598 nm, ε_(max)=12400.

Elemental analysis for C₂₄ H₃₅ N O₅ Si₃

theory: C57.45 H7.03 N2.79 Si16.79 found: C57.44 H7.04 N2.80 Si16.50

Example 8

Preparation of1,4-bis[3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl]propylamino]-anthraquinone:

Leucoquinizarine (2.43 g, i.e. 0.01 mol) andheptamethylaminopropyltrisiloxane (8.37 g, i.e. 0.03 mol) in a mixtureof toluene (50 ml) and N-methylpyrrolidone (20 ml) were refluxed for 2hours. After cooling, a stream of air was bubbled through the reactionmixture for 2 hours. The reaction mixture was poured into water and theorganic phase was washed with water. After column chromatography(eluent: 50/50 heptane/CH₂Cl₂), a mixture of compounds (13) and (14) wasobtained. By crystallization of this mixture from 60 ml of methanol,compound (14) was recovered in the form of a deep-blue powder.

m.p.: 59-60° C.

UV (ethanol) λ_(max)=595 nm, ε_(max)=16 950. λ_(max)=645 nm, ε_(max)=20100.

Elemental analysis for C₃₄ H₆₂ N₂ O₆ Si₆

theory: C53.49 H8.19 N3.67 Si22.07 found: C53.29 H8.08 N3.65 Si22.10

Examples of Dye Compositions Example 9

Locks of natural grey hair containing 90% white hairs were dyed with adye composition containing 5×10⁻² mol of the dye prepared in Example 5,in an amount of a mixture of ethanol and water (90/10 by weight) whichwas sufficient to make the composition up to 100 g.

After treatment for 30 minutes, the hair was rinsed with water for 5minutes and then dried.

The locks of hair were dyed orange-red.

Example 10

Locks of natural grey hair containing 90% white hairs were dyed with adye composition containing 5×10⁻² mol of the dye prepared in Example 7,in an amount of a mixture of ethanol and water (90/10 by weight) whichwas sufficient to make the composition up to 100 g.

After treatment for 30 minutes, the hair was rinsed with water for 5minutes and then dried.

The locks of hair were dyed violet-red.

We claim:
 1. A dye composition for human keratin fibres, comprising atleast one compound of formula (2) or a salt thereof in a medium which issuitable for dyeing:

wherein: each R is the same or different from each other selected fromC₁-C₁₀ alkyl, phenyl, and 3,3,3-trifluoropropyl radicals, at least 80%,in numerical terms, of the radicals R being methyl, u is an integerranging from 1 to 6, t is an integer ranging from 0 to 10, with thecondition that t+u is equal to or greater than 3, and each A denotes aradical independently selected from formula (4a), (4b), (4c), and (4d)below:

wherein: each R₄ independently represents a linear or branched C₁-C₆alkyl radical, OH, C₁-C₄ alkoxy, hydroxy(C₁-C₄)alkyl, COOH, CONH₂, CN,SO₃H, a halogen, an NO₂ radical, or a radical NR₅R₆, wherein R₅ and R₆independently denote a hydrogen atom, a C₁-C₈ alkyl orhydroxy(C₁-C₄)alkyl or amino(C₁-C₄)alkyl radical, or form, together withthe nitrogen atom to which they are attached, a 5- or 6-memberedheterocycle which is interrupted by an oxygen or sulphur atom; m is aninteger ranging from 0 to 2; n is an integer equal to 1 or 2; D is an—SO₂NH—, —CONH— or —O— radical or a radical —NR₇— wherein R₇ is H orCH₃; and W is a divalent radical of formula (5):

or of formula (6): —HC═CH—Z)_(p)—  (6) wherein: R₈ denotes a hydrogenatom, a hydroxyl radical or a linear or branched, saturated orunsaturated, C₁-C₈ alkyl radical, Z is a linear or branched C₁-C₆alkylene radical optionally substituted with an OH radical or a linearor branched, saturated or unsaturated, C₂-C₈ alkoxy radical, and p is aninteger equal to 0 or 1, with the proviso that in formula (2), when (i)A is a group of formula (4a), wherein t is equal to 0, and u ranges from3 to 6, and R₄ is NH₂ and m=0 or 1, and D is NH, then W is a radical offormula (5) other than for which R₈ is H, Z is methylene, and p is equalto 1; (ii) A is a group of formula (4d), wherein t is equal to 3, and uis equal to 1, and R₄ denotes —OCH₃, and m is equal to 1, and D is an—O— radical, then W is a radical of formula (5) other than for which R₈is H, Z is methylene, and p is equal to 1; and (iii) A is a group offormula (4d), wherein t is equal to 0, and u is equal to 4, and R₄ is anNO₂ radical, and m is equal to 1, and D is a radical —NCH₃— then W is aradical of formula (5) other than for which R₈ is H, Z is methylene, andp is equal to
 1. 2. The composition according to claim 1, wherein saidhuman keratin fibres are hair.
 3. The composition according to claim 1,wherein R is selected from methyl, ethyl, propyl, n-butyl, n-octyl, and2-ethylhexyl radicals.
 4. The composition according to claim 3, whereinR is a methyl radical.
 5. The composition according to claim 1, whereint+u ranges from 3 to
 5. 6. The composition according to claim 1, whereinat least one compound of formula (2) or a salt thereof is present in anamount effective to act as a direct dye.
 7. The composition according toclaim 1, wherein said composition has a pH ranging from 4 to
 11. 8. Thecomposition according to claim 1, wherein at least one compound offormula (2) is present in a concentration approximately ranging from0.01 to 10% by weight relative to the total weight of the composition.9. The composition according to claim 1, wherein said medium which issuitable for dyeing comprises water and/or organic solvents inproportions ranging from 0.5 to 20% by weight relative to the totalweight of the composition.
 10. The composition according to claim 9,wherein said organic solvents are selected from alcohols, glycols, andglycol ethers.
 11. A compound of formula (2) or a salt thereof:

wherein: each R is the same or different from each other selected fromC₁-C₁₀ alkyl, phenyl and 3,3,3-trifluoropropyl radicals, at least 80%,in numerical terms, of the radicals R being methyl, u is an integerranging from 1 to 6, t is an integer ranging from 0 to 10, with thecondition that t+u is equal to or greater than 3, and each A denotes aradical independently selected from formula (4a), (4b), (4c) and (4d)below:

wherein: each R₄ independently represents a linear or branched C₁-C₆alkyl radical, OH, C₁-C₄ alkoxy, hydroxy(C₁-C₄)alkyl, COOH, CONH₂, CN,SO₃H, a halogen, an NO₂ radical, or a radical NR₅R₆ wherein R₅ and R₆independently denote a hydrogen atom, a C₁-C₈ alkyl orhydroxy(C₁-C₄)alkyl or amino(C₁-C₄)alkyl radical, or form, together withthe nitrogen atom to which they are attached a 5- or 6-memberedheterocycle which is interrupted by an oxygen or sulphur atom; m is aninteger ranging from 0 to 2; n is an integer equal to 1 or 2; D is an—SO₂NH—, —CONH— or —O— radical or a radical —NR₇— wherein R₇ is H orCH₃; and W is a divalent radical of formula (5):

or of formula (6): —HC═CH—(Z)_(p)—  (6) wherein: R₈ denotes a hydrogenatom, a hydroxyl radical or a linear or branched, saturated orunsaturated, C₁-C₈ alkyl radical, Z is a linear or branched C₁-C₆alkylene radical optionally substituted with an OH radical or a linearor branched, saturated or unsaturated, C₂-C₈ alkoxy radical, and p is aninteger equal to 0 or 1, with the proviso that in formula (2), when (i)A is a group of formula (4a), wherein t is equal to 0, and u ranges from3 to 6, and R₄ is NH₂ and m=0 or 1, and D is NH, then W is a radical offormula (5) other than for which R₈ is H, Z is methylene, and p is equalto 1; (ii) A is a group of formula (4d), wherein t is equal to 3, and uis equal to 1, and R₄ denotes —OCH₃, and m is equal to 1, and D is an—O— radical, then W is a radical of formula (5) other than for which R₈is H, Z is methylene, and p is equal to 1; and (iii) A is a group offormula (4d), wherein i: is equal to 0, and u is equal to 4, and R₄ isan NO₂ radical, and m is equal to 1, and D is a radical —NCH₃—, then Wis a radical of formula (5) other than for which R₈ is H, Z ismethylene, and p is equal to
 1. 12. A process for the dyeing of humankeratin fibres, comprising the step of applying to said fibres a dyecomposition comprising at least one compound of formula (2) or a saltthereof in a medium which is suitable for dyeing:

wherein: each R is the same or different from each other selected fromC₁-C₁₀ alkyl, phenyl and 3,3,3-trifluoropropyl radicals, at least 80%,in numerical terms, of the radicals R being methyl, u is an integerranging from 1 to 6, t is an integer ranging from 0 to 10, with thecondition that t+u is equal to or greater than 3, and each A denotes aradical independently selected from formula (4a), (4b), (4c) and (4d)below:

wherein: each R₄ independently represents a linear or branched C₁-C₆alkyl radical, OH, C₁-C₄ alkoxy, hydroxy(C₁-C₄)alkyl, COOH, CONH₂, CN,SO₃H, a halogen, an NO₂ radical, or a radical NR₅R₆, wherein R₅ and R₆independently denote a hydrogen atom, a C₁-C₈ alkyl orhydroxy(C₁-C₄)alkyl or amino(C₁-C₄)alkyl radical, or form, together withthe nitrogen atom to which they are attached, a 5- or 6-memberedheterocycle which is interrupted by an oxygen or sulphur atom; m is aninteger ranging from 0 to 2; n is an integer equal to 1 or 2; D is an—SO₂NH—, —CONH— or —O— radical or a radical —NR₇— wherein R₇ is H orCH₃; and W is a divalent radical of formula (5):

or of formula (6): —HC═CH—(Z)_(p)—  (6) wherein: R₈ denotes a hydrogenatom, a hydroxyl radical or a linear or branched, saturated orunsaturated, C₁-C₈ alkyl radical, Z is a linear or branched C₁-C₆alkylene radical optionally substituted with an OH radical or a linearor branched, saturated or unsaturated, C₂-C₈ alkoxy radical, and p is aninteger equal to 0 or 1, with the proviso that in formula (2), when (i)A is a group of formula (4a), wherein t is equal to 0, and u ranges from3 to 6, and R₄ is NH₂ and m=0 or 1, and D is NH, then W is a radical offormula (5) other than for which R₈ is H, Z is methylene, and p is equalto 1; (ii) A is a group of formula (4d), wherein t is equal to 3, and uis equal to 1 and R₄ denotes —OCH₃, and m is equal to 1, and D is an —O—radical, then W is a radical of formula (5) other than for which R₈ isH, Z is methylene, and p is equal to 1; and (iii) A is a group offormula (4d), wherein t is equal to 0, and u is equal to 4, and R₄ is anNO₂ radical, and m is equal to 1, and D is a radical —NCH₃—, then W is aradical of formula (5) other than for which R₈ is H, Z is methylene, andp is equal to
 1. 13. The process according to claim 12, wherein saidhuman keratin fibres are hair.
 14. The process according to claim 12,wherein said dye composition is applied to wet or dry keratin fibresand, after said composition has optionally been left on said fibres foran exposure time ranging from 3 to 60 minutes, said fibres are dried,after an optional rinsing operation.
 15. A process for the direct dyeingof human keratin fibres, comprising the step of applying to said fibresa direct dye composition according to claim
 6. 16. The process accordingto claim 15, wherein said human keratin fibres are hair.
 17. The processaccording to claim 15, wherein said dye composition is applied to wet ordry keratin fibres and, after said composition has optionally been lefton said fibres for an exposure time ranging from 3 to 60 minutes, saidfibres are dried, after an optional rinsing operation.